Loud speaker unit



NOV. 22, 1932. A L Ms 1,888,442

LOUD SPEAKER UNIT Filed May 21, 1929 Nov. 22, 1932 PATENT OFFECE ALEXANDER I. ABRAHAMS, OF NEW YORK, N. Y.

LOUD SPEAKER UNIT Application filed May 21,

My invention relates to a new and improved loud speaker unit, and a method of assemblin the same.

One of the objects of my invention is to provide a new and improved loud speaker unit, preferably of the dynamic type, which shall be capable of substantially uniformly reproduc g sounds substantially within the entire audible range.

Brnoter object of my invention is to provide a loud speaker unit which shall be an improvement of the type shown in U. S. Patent No. 1,711,514 dated May 7th, 1929, so as to eliminate all necessity for having a plug in the sound chamber.

Another object of my invention is to provide a loud speaker unit having an improved diaphragm which shall have the necessary stiffness and will also have the necessary flexibility at the points where stiffness and flexibility are desired.

Another object of my invention is to provide a loud speaker unit having a diaphragm provided with a central convex portion which shall e suitably stiffened so as to prevent the development of undesirable vibrations.

Gther objects of my invention will be set forth in the following description and drawing which illustrate a preferred embodiment thereof, it being understood that the above general statement of the objects of my invention is intended merely to generally explain the same and not to limit it in any manner.

Fig. 1 illustrates one embodiment of my invention.

Fig. 2 is a side elevation of the diaphragm used in this embodiment.

F 3 is top view of the diaphragm 3 shown in Fig. 2.

Fig. 4 shows a different embodiment of my invention.

F 4a is a side elevation of the diaphragm shown in Fig. 4.

4.5 Fig. 5 is a top view of the diaphragm shown in Fig. 4.

Fig. 5a is a detail view showing how the parts are assembled.

In the embodiment shown in Fig. 1, a cas- 9 ing 1 is provided having a space 2 in which 1929. Serial No. 364,792.

the usual field coils may be located, a central core 3 being provided which is magnetized by the field current. The casing 1 is provided with the usual cap 4 which is connected to said casing 1 by means of screws 5 so as to form the usual narrow annular gap for the magnotic flux. The diaphragm l) is provided with the usual coil 6. The diaphragm D is preferably stamped from thin metal such as duralumin about .002 of an inch thick.

In the embodiment shown in Fig. 2, the dia phragm D is provided with a peripheral flange 7, an intermediate frusto-conical or convex portion 8, and an outer conical or con vex tip portion 9. Flutes or corrugations 10a are formed in the tip 9. These are wider at their outer ends in order to make allowance for the taper of the outer portion 9 of the diaphragm.

A flexible member 10 made of a suitable non-stretchable and impregnated cloth is connected to the flange 7 and to the intermediate portion 8 by any suitable cement, such as a celluloid cement. The peripheral member 10 preferably extends beyond the flange 7 and it is clamped between gaskets G connected to an intermediate member 11 which is suitably connected to the cap 4. The member 11 is provided with binding posts B which are suitably connected to the coil 6. The device is provided with a throat T which is externally threaded at 14 and this throat T is connected to the intermediate member 11 by means of screws 15. The diaphragm D is caused to vibrate in a piston-like manner when a modulated current is sent through the coil 6. Since the peripheral holding member 10 is imperforate, air waves are produced at the entire outer. surface of the diaphragms. It will be noted that the members T and 11 n which may be considered as forming part of the casing, cooperate to present inner surfaces which generally follow the contour of the diaphragm D, save that the space between the diaphragm D and the adjacent inner surfaces of the members 11 and T gradually in creases, so as to present a tapered passage for the exit of sound waves, said passage increasing in effective cross section according to an exponential formula which is preferably the ill ripheral member 10 and the parts are same as the exponential formula of the horn which is connected to the throat T.

The exponential formula for horns is set forth in the transactions of the National Academy of Sciences, 1919, page 292, and in numerous other publications.

Experience has shown that unless the tip 9 is still, that undesirable vibrations are produced at this part of the diaphragm, which distort the quality of the reproduced sound. It has heretofore been thougat necessary to use a plug in the sound chamber in order to produce uniform reproduction, but I have found that the use of this plug is entirely unnecessary if a properly designed diaphragm and air chamber are employed.

In the embodiment shown in Fi 1, the diaphragm D is made of thin metal previously mentioned, and it is provided with a pesubstantially the same as shown in Fig. 1.

It will be noted in both embodiments the coil 6 is connected to a non-metallic port 18 which is cemented to the inner side of the outwardly projecting part of the diaphra m. The coil-mount 18 can be made of an impregnated strong linen cloth, stiffened by several coats of lacquer, and connected by a celluloid cement to the diaphragm. It could also be made of bakelite, or of a thin, light, stiff paper, such as manuscript paper. If the coil-mount 18 is made of cloth or paper, it is cut to provide serrations S in order to enable it to be bent into the proper frustothat sup-

conical shape at the outer end thereof. The

outer cloth diaphragm mount 10 can be similarly cut and shaped.

In the embodiment shown in Figs. 4-5, the diaphragm D is provided with an intermediate frusto-conical portion 8, but the tip 9a is domeshaped, instead of being conical.

This dome-shaped tip 9a has sufiicient inherent stiffness to make the corrugations 10a unnecessary, and hence said corrugations 10a may be dispensed with, without departing from the invention.

In order to assemble the device, the intermediate member 11 is inverted, the adjacent gasket is placed in a recess in member 11 which is provided for this purpose, the diaphragm is placed in position, the outer gasket (or gaskets) is placed in position, and the parts are then loosely connected by screws 11b to provide a sub-assembly. Vhilc I have shown thediaphragm mount 10 as projecting beyond the peripheral flange of the diaphragm, it would not he departing from my invention if the outer diameter of the peripheral flange of the diaphragm was substantially the same as the outer diameter of the flexible cloth mount, so that the gaskets clamped upon both metal and cloth;

The operator now places the sub-assembly thus formed into the desired central position where he can see the top of the diaphragm at the top thereof. Since the diaphragm pro ects into and above the intermediate cas ing memher 11 while said member 11 is held in said inverted position, an experienced operator can readily center the diaphragm with respect to the intermediate casing n1e1nher 11. The operator then tightens the screws 11?), to securely clamp the diaphragm (to which the coil has been previously tached) in central position. A

The intermediate member 11, having the diaphragm connected thereto, is now inverted to the normal position on a suitable annular support, and the cap inen'iber 1 is placed again st the lower or gaskets G,

and the p rts are adjusted u il the central {1X15 of the C011 6 coincides v .oh the central axis of the oi'iening coil o orcer to conveniently define this assembly in the claims, it will he assumed that the l position of the parts is that shown in F: 1 and 566 for example, although the action of the unit does not deperd upon any particular position. The diaphragm located in a casinghaving a thr and this throat constitutes the opening of said casing. The central part of the daphragm projects forwardly towards this open end of the cas ing so that the central part of the Ciaphragm is generally convex in shape, when it is viewed from the open end of the casing. For example, I do not wish to be limited to the particular type or form of constr ction of the flange of the diaphragm illustrated herein, and in particular, I do not vish to be re-- stricted to the use of the member 10 which projects beyond the flange 7 I have shown a preferrel embodiment of my invention, but it is clear that numerous changes and emissions can be made without departing from its spirit.

I cl. 'm:

1. A speaker unit for a horn comprising a casing having an opening, a diaphrag n located in cas 1g, said diaphragm having a periphery and a central part, the central part of said diaphragm projecting forwardly from said peri r-hery towards the openi of the casing, the wall of said casing adjacent said diaphra 'm being shaped so that the passage between said wall and d diaphragm has an increasing cross-rectional area, said diaphragm having a central portion which is sharply inclined to said pcriphery.

2. A speaker unit for a horn comprising a casing, a diaphragm located within said casing, said casing having an opening, said diaphragm having a peripheral flange, said diaphragm having a forwardly projecting dome-shaped portion of greater stiffness than said flange, said dome-shaped portion being aligned with said opening.

3. In a speaker unit for a horn, a casing having an opening therein, a diaphragm located within said casing and having a peripheral lateral flange, said diaphragm also having a forwardly projecting central portion, said central portion being shaped to be stiffer than said flange, said central por 'on being aligned with said opening.

4. In a speaker unit for a horn, a casing located in said casing, and having a peripiieral lateral flange, saFd diaphragm having a forwardly projecting central portion of tapered shape, the tip of said central portion being more sharply tapered than that part of said central portion which is directly cent said flange.

5. In a speaker unit for a horn, a casing having an opening therein, a diaphragm located in said casing, and having a peripheral lateral flange, said diaphragm having forwardly projecting central portion of tapered shape, the tip of said central portion being more sharply tapered than that part of said central portion which is directly adjacent said flange, said tip having a stiffened wall.

6. A speaker unit for a horn comprising a casing having an opening therein, a diaphragm located in said casing, said casing having an annular space between its inner wall and the adjacent part of said diaphragm, the central part of said diaphragm being aligned with said opening, the cross-section of said annular space increasing towards said opening according to an exponential formula.

7. A speaker unit for a horn comprising a casing having an opening therein, a diaphragm located in said casing, said casing having an annular space between its inner wall and the adjacent part of said diaphragm, the central part of said diaphragm being aligned with said opening, the cross-section of said annular space increasing towards said opening according to an exponential formula, said casing also having a throat at its opening which expands according to said exponential formula.

8. A speaker unit for a horn comprising a casing having an opening therein, a diaphragm located in said casing, said diaphragm having a peripheral lateral flange and a forwardly projecting central portion having a dom e-shape, said central portion be ing aligned with said opening and being corrugated and stiffer than said flange.

9. A speaker unit for a horn having a casing provided with an opening, a perforated cap member located at the opening of said casing and adapted to partially close the same, a second member located above said cap and having an opening which registers with the perforation of said cap, fastening means adapted to connect said diaphragm to the underside of said second member, and additional fastening means adapted to connect said second member to said cap.

10. A speaker unit for a horn having a casing provided with an opening, a perforated cap member located at the opening of said casing and adapted to partially close the same, a second member located above said cap and having an opening which registers with the perforation of said cap, fastening means adapt to connect said diaphragm to the nndei le of said second member, and additional fastening means adapted to connect said second member to said cap, said fastening means comprising members having heads and shanks, the heads being below the shanks.

In testimony whereof I afiiX my signature.

ALEXANDER I. ABRAHAMS.

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